1. Field of the Invention
The present invention relates generally to exercise machines. More particularly, the present invention relates to substantially constant-force resistance modules for use in exercise machines.
2. Related Art
The value of resistance training has been recognized for many years. The goal of most resistance training exercises is to provide resistance to movement by a user such that the user's musculature is strained while displacing a load. So-called “free weights” are perhaps the simplest manner in which to provide this resistance, as a user can simply lift a weight while gravity acts on the mass of the weight to provide resistance to the user's motions. Because the force of gravity is sufficiently constant through a range of motion a human user can replicate, free weights can effectively apply a substantially constant resistance through the range of motion. While free weights are effective in providing a substantially constant force through a range of motion, free weights are necessarily heavy and often bulky, posing the risk of injury to a user and providing an exercise system that can be difficult to move and compactly store.
In addition to free weights, weight systems have been incorporated into machines which often have pulley and handle systems intercoupled to the weight system to allow a variety of resistance training exercises to be performed. Such exercise machines often have a “stack” of weights to which a take-off is provided to allow a user to adjust both the level of weight desired and the type of exercise desired, i.e., bench press, leg curls, etc. Exercise machines utilizing weight systems suffer from many of the problems associated with free weights in that the machines can be very heavy and difficult to move.
For these reasons, exercise machines have been developed that substitute springs or other resistant members for weight systems in an effort to streamline the exercise machine into a lighter and safer machine. Also, springs have been incorporated into exercise machines for use in low-gravity environments, where the gravitational force is sufficiently low as to negate the effectiveness of weight training.
While springs have been used with some success to simulate the resistance provided by free weights or weight systems, springs have also proved problematic as resistance members. This is because most springs generally provide a varying resistance to motion, that is, the force produced by a spring generally changes as the displacement of the spring increases or decreases. Thus, a user may encounter very high or low resistance as the range of motion is begun, and very low or high resistance, respectively, as the range of motion is completed. As the goal of most resistance exercises is to provide constant resistance through a range of motion, conventional springs have thus proved problematic as weight substitutes in exercise equipment.